The process of attaching an end to a body of a metal container is well known in the art and conventionally involves a double seaming process. A double seam is formed by mechanically folding the periphery of the end over a flange of the body to interlock five layers of material together: three layers of the end and two layers of the body. The resulting double seam gives rise to a bulge around the rim of the container.
Before the double seaming process was available, ends were attached to the body of a metal container by soldering. Soldering of containers caused a variety of issues, including foreign contaminants such as lead and other harmful heavy metals. Although the double seaming process is a cheaper and safer alternative to soldering, the bulging double seam is not aesthetically desirable. Moreover, the bulging double seam around the rim of a container is often associated with cheap canned goods. This is a particular concern when the containers are used for decorative purposes for high end products.
A process of attaching an end to a container without using the double seam process is known in the art. FIG. 1 illustrates this process for attaching an end 1 to a body 2 of a metal container to provide a container with a “hidden” seam. The process involves inserting a lip 3 of the end 1 into a partially curled lip 4 of the body 2 to close an opening of the body. Once in position, a curling tool is applied against the partially curled lip 4 of the body, whilst pressing down on the end 1 with a substantially flat reaction tool, to further curl it securely around the lip 3 of the end 1. The process results in clasped lips 5, which attach the end to the body. The definitions of a curling tool and a reaction tool are described in the detailed description below.
In order to form a tight closure, the perimeter of the end 1 must be a tight fit around the inside of the body 2. As such, the end 1 can only be inserted into the body 2 by tilting the end at an angle relative to the body. Subsequent levelling of the end 1 may cause scratching of the internal lacquer.
Thus, it is desirable to provide a process of attaching an end to a body of a container that does not damage the inside of the body, and that produces a “hidden” seam. It is also preferable that the process can be readily automated.